Muscle diseases include many diseases and ailments that either directly, via intrinsic muscle pathology, or indirectly, via nerve or neuromuscular junction pathology, impair the functioning of the muscles. Muscular dystrophy (MD) is a group of muscle diseases that weaken the musculoskeletal system and hamper locomotion. Muscular dystrophies are characterized by progressive skeletal muscle weakness, defects in muscle proteins, and the death of muscle cells and tissue.
Myotonic Dystrophy (DM) is the most prevalent muscular dystrophy in adults, affecting 1/8000 individuals worldwide, and is incurable. There are multiple clinical manifestations of the disease including disabling musculoskeletal symptoms (myotonia, muscle weakness and wasting), ophthalmologic defects (cataract) and cognitive deficits. The genetic abnormality underlying the predominant form, DM1, is caused by a pathological expansion of CTG repeats in the 3′ untranslated region of the DMPK (DM protein Kinase) gene. When transcribed, the expanded CUG entraps trans-acting RNA binding proteins (RBPs) in the cell nucleus, leading to aberrant processing of many downstream RNA targets. The prevailing model mainly focuses on MBNL1 (muscleblind like protein), a splicing factor which is sequestered on the toxic CUG repeats. Mounting evidence from the literature indicates that other factors co-regulate MBNL 1-dependent RNA processing, and thus play a key role in the pathogenesis of DM1.
DM1 is a dominantly inherited neuromuscular disease characterized by progressive myopathy and myotonia, due to large expansions (>50 and up to 4000) of CTG-repeats in the 3′ UTR of the DMPK gene. The disease also results in a combination of heart defects, cataract, GI dysfunction, insulin resistance and cognitive deficits, and is thus complex and generalized. The transcribed CUG-expanded RNAs adopt an abnormal hairpin structure and accumulate in the nucleus as foci, where they entrap, or more indirectly deregulate, RNA processing proteins (RBPs). It is well-established that DM1 is in part caused by the dysfunction of two well-characterized RBPs, MBNL1 and CUGBP1 (CUG binding protein 1, aka CELF1), resulting in a global mis-regulation of splicing events (i.e. ‘spliceopathy’). Aberrant splicing in DM1 leads to the generation of isoforms that are normally found in a different developmental stage (e.g. fetal isoform produced in adult muscle), or in a different tissue (e.g. non-muscle isoform in muscle), and are not functional in the temporal/local cellular context. In addition to missplicing, abnormal translation, subcellular localization and turn-over of RNA targets have been reported in DM1. Studies of corresponding DM1 mouse models have greatly enhanced understanding of the mechanism of the pathologic cascade that underlies the disease. Despite these major advances, it has become increasingly apparent that MBNL1/CUGPB1 functional imbalance does not fully explain DM1 pathophysiology. For example, in MBNL1-deficient mice muscle wasting (as observed in DM1 patients) is not recapitulated, nor is the full spectrum of aberrantly spliced exons that is associated with DM1 in humans. A 2-fold elevation of CUGBP1 levels in transgenic mice (comparable to that observed in DM1 muscle) does not induce changes in alternative splicing. Given that RBPs often act in protein complexes, these observations prompted an active search for additional factors that likely contribute to the disease. Among the candidates, hnRNP H, and more recently Staufen1 have been shown to modulate the MBNL1/CUGBP1-dependent aberrant splicing in DM, but other factors have yet to be uncovered.
Isoprenoid antibiotics were originally isolated from the phytopathogenic fungus Ascochyta viciae. (Sasaki, H. et al., Isolation and structure of ascofuranone and ascofranol, antibiotics with hypolipidemic activity. J Antibiot (Tokyo), 1973, 26:676-680). Among them, ascochlorin and ascofuranone have been shown to be non-toxic compounds. Structurally related compounds have been subsequently isolated from other fungi (e.g., Fusarium, Cylindrocladium, Cylindrocladium ilicicola, Nectria coccinea, Colletotrichum nicotianae, Acremonium luzulae, Cephalosporium diospyri, Verticillium, Cylindrocarpon lucidum, Nigrosabulum globosum, and the insect pathogenic fungus Verticillium hemipterigenum). (Hosono, K. et al., Ll-z1272 alpha epoxide, a precursor of ascochlorin produced by a mutant of ascochyta viciae, J Antibiot (Tokyo), 2009, 62:571-574; Seephonkai, P. et al., A novel ascochlorin glycoside from the insect pathogenic fungus verticillium hemipterigenum bcc 2370, J Antibiot (Tokyo), 2004, 57:10-16).
Ascochlorin and ascofuranone display antitumorigenic properties, both in vitro and in vivo. (Jeong J H, et al. J Cell Biochem. 2012 April; 113(4):1302-13; Kang, J. H. et al. J Biol Chem. 2012 May 4; 287(19):15661-71; Jeong, J. H. and Chang, Y. C., Ascochlorin, an isoprenoid antibiotic, induces g1 arrest via downregulation of c-myc in a p53-independent manner, Biochem Biophys Res Commun., 2010, 398:68-73; Magae, J. et al., Antitumor and antimetastatic activity of an antibiotic, ascofuranone, and activation of phagocytes, J Antibiot (Tokyo), 1988, 41:959-965; Nakajima, H. et al., Aberrant expression of fra-1 in estrogen receptor-negative breast cancers and suppression of their propagation in vivo by ascochlorin, an antibiotic that inhibits cellular activator protein-1 activity. J Antibiot (Tokyo), 2007, 60:682-689). In a murine model of mammary carcinoma, it was demonstrated that intraperitoneal administration of ascochlorin significantly suppressed cancer growth and prolonged survival. (Nakajima et al., 2007).
In addition to anticancer properties, ascochlorin and its derivatives exhibit a wide range of physiological activities, including antimicrobial/antiviral activity, trypanocidal properties, hypolipidemic activity, suppression of hypertension, improvement of type I and II diabetes, and immunomodulation. (Yabu, Y. et al., The efficacy of ascofuranone in a consecutive treatment on trypanosoma brucei brucei in mice, Parasitol Int. 2003, 52:155-164; Hosono et al., 2009).
There exists a need for non-toxic compounds for the treatment of muscle diseases.